1. Field of the Invention
This invention relates to the production of a new class of epoxy derivative compositions and, more particularly, is concerned with a process for equalizing the reactivity rate between the alpha and beta carbons of a terminal epoxy group of an epoxy-containing compound to alter the reactivity of said epoxy-containing compound in an aqueous system. The invention also contemplates the production of stable, film-forming aqueous dispersions of a mixture of an epoxy containing compound and an acrylic polymer including a group reactive with the epoxy compound. Such mixtures, upon drying in air, provide tough, flexible compositions having thermoplastic memory and other desirable physical characteristics.
2. Description of the Prior Art
Aqueous dispersions of epoxy resins are well known, commercially available materials having wide applicability in the coating field. Generally speaking, such aqueous dispersion systems of epoxy resins are sold as two separate components. Prior to use, the two components are admixed, and must be used before the combined mix cures into an isoluble, infusible mass. Thus, aqueous, epoxy-based single component coating compositions characterized by extended shelf life have simply been unavailable in the prior art.
Water based acrylic polymer dispersions for use in coating applications and as paints are also known. See, e.g., U.S. Pat. No. 2,795,564 - Conn et al. The resulting coatings produced from such acrylic dispersions generally have good color and color retention and satisfactory resistance to water-borne stains, as well as possess other desirable properties. In general, such acrylic dispersions have found utility as water-based paints and are well known, commercially available materials made for that purpose.
While numerous attempts have been made in an effort to combine the desirable characteristics of epoxy resins with the desirable characteristics of acrylate esters (see e.g., U.S. Pat. Nos. 3,238,170 - Wolf et al; 3,288,884 - Sonnabend et al; 3,291,857 - Howerton; 3,390,114 - Uhl; 3,418,392 - Leitner; 3,466,347 - David; 3,513,222 - Speitel; 3,519,702 - Wear; 3,563,929 - Guldenpfennig; and 3,657,381 - Speitel) no single component, aqueous dispersion of a combination of epoxy and acrylate polymer mixtures having extended shelf life characteristics have heretofore been prepared in the prior art.
In studies of active sites of epoxy compounds by crystal X-ray microscopy, it was found that the oxirane oxygen is bound to the beta carbon in a shorter bond than to the alpha carbon: ##STR1## where R is a hydrocarbon radical. Investigators have learned that the reactivity of the above epoxy configuration in aqueous media will be such that the primary reaction always involves the beta carbon atom: ##STR2## See W. C. J. Ross, 1950 Journal of Chemical Society, London, Eng. pp. 2257-2272; A. J. Durbetaki, Analytical Chemistry, Vol. 28 No. 12, December 1956, pp. 2000-2001; Analytical Chemistry, Vol. 30 No. 12, December 1958, pp. 2024, 2025; B. D. Sully, Analyst, Vol. 85, December 1960, pp. 895-897; R. R. Jay, Analytical Chemistry, Vol. 36 No. 3, March 1964, pp. 667-668; G. A. Stenmark, Analytical Chemistry, Vol. 29 No. 9, September 1957, pp. 1367-1369.
Where, as may be the case in aqueous acrylic dispersion systems, contaminating ionic material, such as free halides, are present, the secondary reaction of the epoxy derivative compound resulting from the primary reaction will involve a salinification, i.e., the free halide will attach to the alpha carbon atom, and the further activity of the epoxy-derivative group is inhibited completely. As a consequence, it has not been possible to provide stable, epoxy-acrylic dispersion systems.